Adelson is a casino magnate with gaming empires in Nevada and Asia and vast media control in Israel.

In comparison, President Barack Obama’s largest donator is Dreamworks chief executive and Hollywood producer Jeffrey Katzenberg, who donated $2.5 million.

The Washington Post says the calculated cost of this election will be the most expensive to date, costing $700 US million more than 2008.

A $6 billion total cost is forecast by the Center for Responsive Politics.

Sheila Krumholz, executive director of the Center for Responsive Politics said: “We’re seeing historic spending levels spurred by outside groups dominated by a small number of individuals and organizations making exceptional contributions.”

The new Super Political Action Committees have spurred campaign donations, due to a decision passed by the US Supreme Court in 2010.

A New York Times definition says a SuperPAC allows “unlimited amounts of money outside of federal contribution limits, from rich people, unions and corporations, pool it all together and spend it to advocate for a candidate, as long as they are independent and not coordinated with the candidate.”

The majority of donations has been spent on television advertising by both candidates.